: Mutations in oncogenes and tumor suppressor genes affect tumor progression, recurrence and response to therapy. In order to obtain a meaningful genotype for many of these genes, it is necessary to scan the complete coding sequence and splice sites for mutation. And yet, due to the heterogeneous nature of tumors and tumor DNA samples, the established methods for tumor genotyping give significant levels of false negative results - i.e., many mutations in the genes of interest are missed. Without a tumor genotyping technology that is comprehensive and reliable, basic studies that might identify correlations between tumor genotype and disease progression and/or response to therapy cannot be performed adequately. Peptide Mass Signature Genotyping (PMSG) can remedy this inadequacy because it is sensitive enough to identify minority mutations in tumor samples that are missed by currently established methods. The goal for the proposed SBIR project is to develop a PMSG test that is performed entirely in vitro. The new test will be faster than the current in vivo test and will be more amenable to miniaturization and automation. The target gene for test development will be TP53, a gene that is mutated in most cancers, and in which cancer related mutations can occur at thousands of different positions. The TP53 gene will be the focus of the SBIR project, but the genotyping system that will be developed will be applicable to any gene or set of genes, whether involved in cancer or not.